Shock describes matter subject to extreme rates of force with respect to time. Shock is a vector that has units of an acceleration (rate of change of velocity). The unit g (or g) represents multiples of the acceleration of gravity and is conventionally used.

A shock pulse can be characterised by its peak acceleration, the duration, and the shape of the shock pulse (half sine, triangular, trapezoidal, etc.). The Shock response spectrum is a method for further evaluating a mechanical shock.[1]

Field shocks are highly variable and often have very uneven shapes. Even laboratory controlled shocks often have uneven shapes and include short duration spikes; Noise can be reduced by appropriate digital or analog filtering.[13][14]

Governing test methods and specifications provide detail about the conduct of shock tests. Proper placement of measuring instruments is critical. Fragile items and packaged goods respond with variation to uniform laboratory shocks;[15] Replicate testing is often called for. For example MIL-STD-810G Method 516.6 indicates: ‘’at least three times in both directions along each of three orthogonal axes”.

A brittle or fragile item can fracture. For example, two crystal wine glasses may shatter when impacted against each other. A shear pin in an engine is designed to fracture with a specific magnitude of shock. Note that a soft ductile material may sometimes exhibit brittle failure during shock due to time-temperature superposition.

A ductile item can be bent by a shock. For example, a copper pitcher may bend when dropped on the floor.

Some items may appear to be not damaged by a single shock but will experience fatigue failure with numerous repeated low-level shocks.

A shock may result in only minor damage which may not be critical for use. However, cumulative minor damage from several shocks will eventually result in the item being unusable.

A shock may not produce immediate apparent damage but might cause the service life of the product to be shortened: the reliability is reduced.

A shock may cause an item to become out of adjustment. For example, when a precision scientific instrument is subjected to a moderate shock, good metrology practice may be to have it recalibrated before further use.

Some materials such as primary high explosives may detonate with mechanical shock or impact.